Billiard Ball question
Lewis Stiller
Hi, I have a question about The Billiard Ball. Given the premise that
objects in a zero-gravity field move at velocity c relative to the
spectators, I don't understand how the ball itself was accelerated to
this speed.
This is because, the ball enters the field at some finite, rather slow
speed, right? Isn't the field turned on all the time and the ball
enters it.
Then, say 1 millisecond after the edge of the ball has entered the
field, will not just the edge of the ball have accelerated to c? I'm
not quite sure what would happen.
The point is, that the story gives the impression of a billiard ball
traveling very fast, but in fact it is much more complicated, because
at first only the very edge of it is accelerated.
For that matter, what exactly would the effects of a billiard ball
traveling that fast be? Say, .999 c?
Another question: I might be able to assume that the billiard ball
experiment was the very first one with zero-gravity and a solid. I
find this implausible, but I can accept it. But, why weren't the
effects noticed during the Brazil demonstration or the .82g
demonstration ? Wouldn't a solid not fall to directly to earth when
placed in such a field if we accept the hypotheses of the story? Or is
there something fundamentally different between .82g and 0 g that
affects the science?
--
Lewis Stiller
Dept. of Computer Science, The Johns Hopkins University
Baltimore, MD 21218-2194
email: sti...@cs.jhu.edu
Andrew C. Plotkin
question Lewis Sti...@rhombus.cs (1446)
> Hi, I have a question about The Billiard Ball. Given the premise that
> objects in a zero-gravity field move at velocity c relative to the
> spectators, I don't understand how the ball itself was accelerated to
> this speed.
> This is because, the ball enters the field at some finite, rather slow
> speed, right? Isn't the field turned on all the time and the ball
> enters it.
> Then, say 1 millisecond after the edge of the ball has entered the
> field, will not just the edge of the ball have accelerated to c? I'm
> not quite sure what would happen.
If you assume that each particle begins moving at c in the direction
it's moving when it enters the field, then you wind up with a stream of
high-energy cosmic rays going *down*. (The leading edge of a rolling
ball moves down.) As more of the ball is worn away, the geometry
changes, and I think you wind up irradiating pretty much everything
below the billiard table. Since they were high up in a building over a
city, you probably kill off the city. (A billiard ball is a *lot* of
protons and such.)
If you take into account random molecular motion, then the particles
come out in *all* directions, and everyone dies.
> For that matter, what exactly would the effects of a billiard ball
> traveling that fast be? Say, .999 c?
Asimov didn't specify exactly what happened when the particles leave the
field. Presumably they emit Cerenkov radiation and slow down "a little."
How much? You sort of have to know to make predictions.
> Or is
> there something fundamentally different between .82g and 0 g that
> affects the science?
That is the implication of the story, yes. It was the 0.0 g field that
produced all the weird effects. Before you reach the zero point, the
particles in the field are not zero-mass, therefore they don't do the
speed-of-light thing.
Conclusion: The physics is a little implausible, but the story is still good.
--Z
"And Aholibamah bare Jeush, and Jaalam, and Korah: these were the
borogoves..."
Mark 'Henry' Komarinski
: Hi, I have a question about The Billiard Ball. Given the premise that
: objects in a zero-gravity field move at velocity c relative to the
: spectators, I don't understand how the ball itself was accelerated to
: this speed.
: This is because, the ball enters the field at some finite, rather slow
: speed, right? Isn't the field turned on all the time and the ball
: enters it.
: Then, say 1 millisecond after the edge of the ball has entered the
: field, will not just the edge of the ball have accelerated to c? I'm
: not quite sure what would happen.
I think a reader suggested this to Asimov at one point. Can't remember
what he said about it tho.
: The point is, that the story gives the impression of a billiard ball
: traveling very fast, but in fact it is much more complicated, because
: at first only the very edge of it is accelerated.
: For that matter, what exactly would the effects of a billiard ball
: traveling that fast be? Say, .999 c?
Two things would have happened. First, the sonic boom created by
the ball travelling at .999c would at the very least kill anyone in the room,
maybe destroy the building also.
Second, the ball wold probably not make it to outer space (as the story
suggested) because it would have burned up long before then.
: Another question: I might be able to assume that the billiard ball
: experiment was the very first one with zero-gravity and a solid. I
: find this implausible, but I can accept it. But, why weren't the
: effects noticed during the Brazil demonstration or the .82g
: demonstration ? Wouldn't a solid not fall to directly to earth when
: placed in such a field if we accept the hypotheses of the story? Or is
: there something fundamentally different between .82g and 0 g that
: affects the science?
At 0g, the object has supposedly no mass (the way it was implemented)
the only thing that can have no mass is electromagnetic waves.
Electromagnetic waves run at the speed of light.
When the objects have .82g, they still have mass and therfore do
not exit at the speed of light.
-Mark
James Nicoll + Jasmine
>
>If you assume that each particle begins moving at c in the direction
>it's moving when it enters the field, then you wind up with a stream of
>high-energy cosmic rays going *down*. (The leading edge of a rolling
>ball moves down.) As more of the ball is worn away, the geometry
>changes, and I think you wind up irradiating pretty much everything
>below the billiard table. Since they were high up in a building over a
>city, you probably kill off the city. (A billiard ball is a *lot* of
>protons and such.)
>
>If you take into account random molecular motion, then the particles
>come out in *all* directions, and everyone dies.
Heh. If the billiard ball is moving close to the speed of light
as it exits the field (0.99 C, say), if even 1% of its energy is released
as it passes through the person it killed, and the wall(s) behind him,
everyone is dead: a 100 gram object has around 4x10**18 Joules of kinetic
energy at that velocity (roughly a gigaton of TNT). That should put a bit of
a ding in the city, as well.
James Nicoll
--
If mail bounces, try jdni...@engrg.uwo.ca
"I'm not deaf. The world is muffled."
Lewis Stiller
Mark 'Henry' Komarinski <koma...@craft.camp.clarkson.edu> wrote:
>Lewis Stiller (sti...@rhombus.cs.jhu.edu) wrote:
>
>: Another question: I might be able to assume that the billiard ball
>: experiment was the very first one with zero-gravity and a solid. I
>: find this implausible, but I can accept it. But, why weren't the
>: effects noticed during the Brazil demonstration or the .82g
>: demonstration ? Wouldn't a solid not fall to directly to earth when
>: placed in such a field if we accept the hypotheses of the story? Or is
>: there something fundamentally different between .82g and 0 g that
>: affects the science?
>
>At 0g, the object has supposedly no mass (the way it was implemented)
>the only thing that can have no mass is electromagnetic waves.
>Electromagnetic waves run at the speed of light.
>When the objects have .82g, they still have mass and therfore do
>not exit at the speed of light.
>
>-Mark
>
Yes, I did not claim it would. What I am wondering is the following, which
I thought my first post made clear, but apparently not.
The original problem was that Bloom had incorrectly considered
that diminuition of gravity would only affect the force between the
object and the earth, so that the object would be pulled to the
earth with less force, i.e., have fractional g.
In fact, as Priss points out, the physics of the situation demand that
the object have less gravity with respect to all bodies. So that, at .82 g,
say, an object that is released would not fall to earth in a straight line
but would follow some eccentric path. I am not claiming it would fall
at the speed of light only that its fall would not be straight. And this
property would have clued Bloom in to realize that the billiard ball
would not hover at 0 g but would be emitted.
Michael Friedman
>Hi, I have a question about The Billiard Ball. Given the premise that
>objects in a zero-gravity field move at velocity c relative to the
>spectators, I don't understand how the ball itself was accelerated to
>this speed.
Since I didn't read the story, I can't comment. The idea seems rather
bizarre, however. We all know that a ball in 0 g just floats there.
>For that matter, what exactly would the effects of a billiard ball
>traveling that fast be? Say, .999 c?
A very large explosion.
Tom O Breton
> Hi, I have a question about The Billiard Ball. Given the premise that
> objects in a zero-gravity field move at velocity c relative to the
> spectators,
> will not just the edge of the ball have accelerated to c?
We could suppose that the edge of the ball "yanks" the rest of it along.
That won't hold up, though - I doubt it could have that much tensile
strength.
But... we don't have to assume that the edge of the field is perfectly
sharp. Maybe there is no point at which the tidal effect exceeds the
tensile strength of the ball.
> Or is there something fundamentally different between .82g and 0 g that
> affects the science?
I believe Asimov's premise was that, yes, 0 g is a fundamentally
different.
Tom
--
The Tom spreads its huge, scaly wings and soars into the sky...
(t...@world.std.com, TomB...@delphi.com)
Sam Sebastian Laur
Lewis Stiller <sti...@rhombus.cs.jhu.edu> wrote:
>This is because, the ball enters the field at some finite, rather slow
>speed, right? Isn't the field turned on all the time and the ball
>enters it.
Well, I read this story as a part of a short story collection, called
"Robot Dreams", which had some explanations on every story by Asimov.
On this particular occasion, he *knew* that the physics of the story
wasn't quite right (he realised, too, that the ball would be torn into
N+1 parts, entering the field bit by bit). So he thought that it
wouldn't matter, as the 0.0 g field would itself be quite impossible
to make...
--
/* Sam Laur sl...@utu.fi */
/* Go finger yourself! */
John H. Rickert
> field, will not just the edge of the ball have accelerated to c? I'm
> not quite sure what would happen.
I'd guess that a thin layer was ripped off and that a fraction of a second
later enough of the ball was inside the field that the whole thing was
accelerated (It was pulled along by electromagnetic attraction).
> Another question: I might be able to assume that the billiard ball
> experiment was the very first one with zero-gravity and a solid. I
> find this implausible, but I can accept it. But, why weren't the
> effects noticed during the Brazil demonstration or the .82g
> demonstration ? Wouldn't a solid not fall to directly to earth when
> placed in such a field if we accept the hypotheses of the story? Or is
> there something fundamentally different between .82g and 0 g that
> affects the science?
The effects that would pull it off a straight line are much smaller that
82g. The largest I can find is the accelaration due to the rotation of the
earth which seems to come in at about .004g (quick calculation could be
wrong).
And the point made about the 0g field was that it removed the mass from the
objects. If the field hadn't reached 0g then the object would have had mass
and not traveled at the speed of light..
john rickert
ric...@nextwork.rose-hulman.edu
Jamie McDonald
: Another question: I might be able to assume that the billiard ball
: experiment was the very first one with zero-gravity and a solid. I
: find this implausible, but I can accept it. But, why weren't the
: effects noticed during the Brazil demonstration or the .82g
: demonstration ? Wouldn't a solid not fall to directly to earth when
: placed in such a field if we accept the hypotheses of the story? Or is
: there something fundamentally different between .82g and 0 g that
: affects the science?
My question with "The Billiard Ball" has always been concerned with
what (should have) happenned *before* the ball entered the field. It
seems that once the field was turned on the dust and even the air
within the field should have fallen prey to the same effect which
tossed the pool ball through the body. The dust at least should have
been perforating the folks and objects standing about ntticably,
especially if accelerated at the same rate as the pool ball.
--
shr...@camelot.bradley.edu Jamie McDonald <><
STD Secretary
Mark 'Henry' Komarinski
: In article <1993Sep14....@news.clarkson.edu>,
: Mark 'Henry' Komarinski <koma...@craft.camp.clarkson.edu> wrote:
: >Lewis Stiller (sti...@rhombus.cs.jhu.edu) wrote:
: >Electromagnetic waves run at the speed of light.
: >When the objects have .82g, they still have mass and therfore do
: >not exit at the speed of light.
: >
: >-Mark
: >
: Yes, I did not claim it would. What I am wondering is the following, which
: I thought my first post made clear, but apparently not.
: The original problem was that Bloom had incorrectly considered
: that diminuition of gravity would only affect the force between the
: object and the earth, so that the object would be pulled to the
: earth with less force, i.e., have fractional g.
: In fact, as Priss points out, the physics of the situation demand that
: the object have less gravity with respect to all bodies. So that, at .82 g,
: say, an object that is released would not fall to earth in a straight line
: but would follow some eccentric path. I am not claiming it would fall
: at the speed of light only that its fall would not be straight. And this
: property would have clued Bloom in to realize that the billiard ball
: would not hover at 0 g but would be emitted.
That's the beauty of the ending...you'll never know what was known about
0g before the test took place. Was it truly murder? :)
--
- Mark Komarinski - koma...@craft.camp.clarkson.edu
Ask me about linux, the least expensive UN*X you'll ever see.
julius yang
components. Now, if you accept the premise that the field accelerates
anything in it to lightspeed (which is patently false by modern physics and
thus the sticking point), I feel that the particles are ejected in the
direction that they were going initially at lightspeed. Since they
are traveling so fast, they will move in a straight line at least for
the first 10^-12 seconds or so (the time the particles would take
to exit the building), and punch the hole described.
IMHO, the objection of a massive energy explosion occurring is wrong because
of an analogy: Shoot a bullet through tissue paper. Does the tissue
ignite from the energy absorbed? I'm no gunner, nor have I
done calculations involving momentum transfer, friction, bla bla bla,
but this seems reasonable to me. And so all I need to enjoy the story
is a mild suspension of disbelief, rather than a huge one.
Vance Ashlin
Greetings,
Can I ask a simple question of this group? (I will anyway) :)
What is the name of the Asimov book that 'Billiard Ball' question is
being derived from?
Vance
-------------------------------------------------------------------
Thinking is dangerous, subversive, mindnumbing and leads you astray
ash...@ironbark.ucnv.edu.au
i88...@redgum.ucnv.edu.au
-------------------------------------------------------------------
David Alpert
In article <CDC5u...@blaze.cs.jhu.edu>, sti...@rhombus.cs.jhu.edu (Lewis Stiller) writes...
>
>Hi, I have a question about The Billiard Ball. Given the premise that
>objects in a zero-gravity field move at velocity c relative to the
>spectators, I don't understand how the ball itself was accelerated to
>this speed.
>
>This is because, the ball enters the field at some finite, rather slow
>speed, right? Isn't the field turned on all the time and the ball
>enters it.
>
>Then, say 1 millisecond after the edge of the ball has entered the
>field, will not just the edge of the ball have accelerated to c? I'm
>not quite sure what would happen.
So it's an ellipse while moving fast. That doesn't affect the story.
>The point is, that the story gives the impression of a billiard ball
>traveling very fast, but in fact it is much more complicated, because
>at first only the very edge of it is accelerated.
>
>For that matter, what exactly would the effects of a billiard ball
>traveling that fast be? Say, .999 c?
>
>Another question: I might be able to assume that the billiard ball
>experiment was the very first one with zero-gravity and a solid. I
>find this implausible, but I can accept it. But, why weren't the
>effects noticed during the Brazil demonstration or the .82g
>demonstration ? Wouldn't a solid not fall to directly to earth when
>placed in such a field if we accept the hypotheses of the story? Or is
>there something fundamentally different between .82g and 0 g that
>affects the science?
Yeah. The law relating mass and speed has mass increase as speed increases.
It explains why you can't reach c (see "Impossible, That's All" by guess who in
"Asimov on Science: A 30-Year Retrospective"). The thing is that the equation
also says that if you have a mass, you can't go c, but if you have no mass, you
have to go at c. At .82g you still have a mass. It's easier to accelerate
yourself, but there's no instant speed of light thing. However, at 0 gravity,
you then have NO mass, and there's no way you can keep from going at c.
--
"Infinity occurs at negative five."
- PHYC.LAN.1
Daniel Quinlan
>>>>> jdni...@engrg.uwo.ca (James Nicoll + Jasmine) said:
> Heh. If the billiard ball is moving close to the speed of light
> as it exits the field (0.99 C, say), if even 1% of its energy is released
> as it passes through the person it killed, and the wall(s) behind him,
> everyone is dead: a 100 gram object has around 4x10**18 Joules of kinetic
> energy at that velocity (roughly a gigaton of TNT). That should put a bit of
> a ding in the city, as well.
Yes, it might have that much energy, but nothing even close to 1% of
its energy (by many orders of magnitude) would be released through the
person, the wall, and the city. It passed through the man like
butter, it probably didn't even slow down in a noticable manner. It
would probably pass right through the entire city, leaving the
atmosphere and the Earth (within 10-100 miles, I don't feel like doing
the trig, but you can if you are bored) due to the Earth's curvature.
It is very very roughly equivalent to shooting a bullet through a
light drape.
Dan
--
Daniel Quinlan <qui...@spectrum.cs.bucknell.edu>
--
--
Daniel Quinlan <qui...@spectrum.cs.bucknell.edu>
David Alpert
In article <1993Sep14.1...@oracle.us.oracle.com>, mfri...@us.oracle.com (Michael Friedman) writes...
>In article <CDC5u...@blaze.cs.jhu.edu> sti...@rhombus.cs.jhu.edu (Lewis Stiller) writes:
>
>>Hi, I have a question about The Billiard Ball. Given the premise that
>>objects in a zero-gravity field move at velocity c relative to the
>>spectators, I don't understand how the ball itself was accelerated to
>>this speed.
>
>Since I didn't read the story, I can't comment. The idea seems rather
>bizarre, however. We all know that a ball in 0 g just floats there.
Read the story. This is just the common misconception about 0g. Space is not
zero gravity. Objects still have mass in orbit, and are affected by the pull
of gravity. However, they are in constant freefall (by the time the ship falls
far enough to hit the earth, it has already moved far enough so it falls around
the edge, and the it falls, but it has already moved far enough, etc. ZERO
GRAVITY means zero mass. Something with zero mass, according to some equation
you can read about in _Asimov On Science: A 30 Year Retrospective_ in the
article "The Luxon Wall", must go at the speed of light or violate the laws of
physics. So the ball exits at the speed of light (after that come the holes in
the story, such as the particles would go in all direction because of
uncertainty, and the shock wave of it hitting the wall would obliterate the
whole city, but it still would go out at c.)
ez00...@chip.ucdavis.edu
A zero gravity field does not mean that an object must move at c. It is true
that *massless* particles must move at c, but the absense of a gravitational
field does not make something massless.
Wade
Robert Krawitz
A zero gravity field does not mean that an object must move at c. It
is true that *massless* particles must move at c, but the absense of
a gravitational field does not make something massless.
Even in the absence of an external gravitational field, an object with
mass will generate its own gravitational field. If a ZG field is able
to suppress the gravitational field generated by an object within it,
that object is effectively massless.
On the other hand, since energy is equivalent to mass, energy itself
generates a gravitational field, so it would seem that an object within
a ZG field would have zero mass and zero energy.
--
Robert Krawitz <r...@think.com> OS/IO Software Engineer (617)234-2116
Thinking Machines Corp. 245 First St. Cambridge, MA 02142
Member of the League for Programming Freedom -- mail l...@uunet.uu.net
Tall Clubs International -- tci-r...@think.com or 1-800-521-2512
Leif Magnar Kj|nn|y
Uh, I actually don't think the ball would get very far. See, it would
keep hitting obstacles -- such as the guy who stood in its path, the
walls, and the bleedin' air molecules and dust motes if nothing else
-- and at a relative velocity of 0.999 c (or however many 9's there
were), even a single air molecule would pack enough kinetic energy
relative to the ball to disrupt at least several of the molecular
bonds and stuff that keep the ball in one piece. So, what happens is
that the ball leaves the zero-mass field (zero mass, not just zero
gravity; note that if the field is not in a vacuum, all of the air
molecules etc. inside it will do the same thing as the ball), hits
the air outside the field more or less as if the air was a brick wall,
and disintegrates violently. Just about all of the ball's kinetic
energy is released, most ultimately in the form of heat. The result
is a titanic explosion.
Now, there's still the issue of just *where* that energy came from in
the first place.... if it just appeared out of nowhere, the zero-mass
field could conceivably be used to provide a Free Lunch, and if it
came from the energy needed to set up and maintain the zero-mass
field, then you would need enormous amounts of energy to do so....
I have actually read the story which sparked this debate, but it's
been a while.
-Leif.
--
Leif Kj{\o}nn{\o}y (in LaTex-ese, that is). lei...@lise.unit.no
GS d- -p+ c++ l m* s++/++ g+/- w+ t- r++ (x+) (GeekCode version 0.3)
Save the Whales -- from Greenpeace. Trust noone, keep your harpoon handy.
Cerebus for Dictator!
Lars Knudsen
Having just read the Billiard Ball story and followed the discussion
that has happened here for the past month or so, let me offer a few
ideas and questions.
When the ball very slowly enters the no mass field it has a little
kinetic energy: Ek=1/2*m*v^2
For this to be correct v has to be much slower than c which is indeed
the case.
When the ball starts entering the field what would happen ? As the
first infinitesimal part enters it looses mass and therefore according
to our previous calculations it gains speed. Lets call the
infinitesimal small part of the mass dm and we get: dEk = 1/2*dm*v^2
This is a very small energy, certainly to small to break up the ball,
so it will be used to accelerate the entire ball, thus giving it:
Ek = 1/2*(m-dm)*v'^2.
As more and more of the ball passes into the field the mass is reduced
and the speed increases until finally the entire ball is in the field
travelling at a speed of c.
On the other side of the field the exact opposite thing happens. A
small part passes out of the field, gains wheight and slows the whole
ball down, effectively leaving the field at the same speed as it came
in.
- Lars
Daniel Quinlan
David writes:
> Yeah. The law relating mass and speed has mass increase as speed
> increases. It explains why you can't reach c (see "Impossible,
> That's All" by guess who in "Asimov on Science: A 30-Year
> Retrospective"). The thing is that the equation also says that if
> you have a mass, you can't go c, but if you have no mass, you have
> to go at c. At .82g you still have a mass. It's easier to
> accelerate yourself, but there's no instant speed of light thing.
> However, at 0 gravity, you then have NO mass, and there's no way you
> can keep from going at c.
Wrong. At 0 gravity you have no weight, but you still have the same
mass that you had when you are at 1 G or any G. Any object with any
amount of mass (such as a billiard ball or anything made of
atoms/quarks/leptons/etc.) can never reach speed c. Period.
This can be easily seen looking at basic Lorentz transformations such
as the mass (for relativistic speeds, speeds close to c) equation:
m
m' = -----------------
sqrt(c^2 - v^2)
v and c are in units where the speed of light (c) = 1
m' is the mass in the inertial frame of reference
m is the mass at rest
v is the velocity of the mass as observed by the observer at rest
c is the speed of light (c=1)
You can easily see that as the velocity approaches c, the mass
approaches infinity (since the denominator -> zero) and to accelerate
an object with almost infinite mass (v = .999c) it would take an
almost infinite amount of energy. You can see it gets worse the
closer you are to c. Hence, you can't ever hit c if you have mass.
To give a proper explanation, I should have used the Lorentz
transformation for relativistic momentum. The above should be fairly
clear although it takes a little more thought than some of the more
complex Lorentz transformations (which work better for the "why can't
a spaceship go at the speed of light" problem.)
This problem is also why authors invent things like Hyperspace, Warp,
and mass->tachyon->mass conversions.
Michael Friedman
>In article <1993Sep14.1...@oracle.us.oracle.com>, mfri...@us.oracle.com (Michael Friedman) writes...
>>In article <CDC5u...@blaze.cs.jhu.edu> sti...@rhombus.cs.jhu.edu (Lewis Stiller) writes:
>>>Hi, I have a question about The Billiard Ball. Given the premise that
>>>objects in a zero-gravity field move at velocity c relative to the
>>>spectators, I don't understand how the ball itself was accelerated to
>>>this speed.
>>Since I didn't read the story, I can't comment. The idea seems rather
>>bizarre, however. We all know that a ball in 0 g just floats there.
>Read the story. This is just the common misconception about 0g. Space is not
>zero gravity. Objects still have mass in orbit, and are affected by the pull
>of gravity. However, they are in constant freefall
David, I suggest that you stop getting your physics from science
fiction. Xg is convenient shorthand for the ratio between the weight
of a point object in the circumstances being described and its weight
at rest on Earth at sea level. (And please don't play games with the
meaning of "at rest".) When we say someone (or something) is at 0g we
mean that it undergoes no gravitational acceleration relative to the
reference frame we are using. It has nothing to do with whether the
object has mass or if they are affected by the pull of gravity.
Moreover, your patronizing attitude is extremely irritating,
expecially given your own apparent ignorance.
>Something with zero mass, according to some equation
>you can read about in _Asimov On Science: A 30 Year Retrospective_ in the
>article "The Luxon Wall", must go at the speed of light or violate the laws of
>physics. So the ball exits at the speed of light (after that come
>the holes in the story, such as the particles would go in all
>direction because of uncertainty, and the shock wave of it hitting
>the wall would obliterate the whole city, but it still would go out at c.)
Well, first off, the original question was about a 0g field, not a 0
mass field. Secondly, I think that your ignorance is showing again.
If entering the massless field instantaneously accelerates the ball to
light speed shouldn't exiting instantaneously slow it back down?
Moreover, unless out 0 mass field pumps and incredible amount of
energy into the ball, the atoms in the ball will not have the energy
to break their bonds. In fact, that makes sense. As the particles in
the ball become massless the acceleration exerted by the
electromagnetic fields in the ball should approach infinity. (F = ma.
F stays constant, m-> 0, therefore, a -> oo). In short, we should
expect the ball to stay together. It should travel to the edge of the
field, accelerate to light speed as it traverses the edge, and then
decelerate as it hits the other edge. No radiation, no sonic boom, no
danger.
Michael Fuller
Just a note that this discussion (interesting as it is) is probably
more appropriate for rec.arts.sf.science than r.a.s.written. You'll
also likely to get more interesting hard(-ish) science responses there.
Michael
Tom O Breton
qui...@virgo.cs.bucknell.edu (Daniel Quinlan) writes:
> Wrong. At 0 gravity you have no weight, but you still have the same
> mass that you had when you are at 1 G or any G. Any object with any
> amount of mass (such as a billiard ball or anything made of
> atoms/quarks/leptons/etc.) can never reach speed c. Period.
Asimov knew perfectly well that the premise was scientifically wrong.
It's Science Fiction, and for better or worse, in the genre we accept a
certain amount of fast-and-loose handling of the science involved.
Now, I'm not saying that it's always OK -- I can't count the number of
times I've "corrected" the TV screen when ST:TNG is on, when they've got
their science dead wrong and don't seem to know it, or when they use
terminology that actually means something (and *not* what they think it
does.)
But in Asimov's Billiard Ball, Asimov makes a nice, slim, small-profile
change to the laws of Relativity, and he clearly knows where he's
parting company with real physics and handles it in a way that doesn't
shatter the story's believability even for those who know it's wrong.
Ed Seiler
mfri...@us.oracle.com (Michael Friedman) wrote:
> In article <1993Sep18....@peavax.mlo.dec.com> col...@powdml.enet.dec.com (David Alpert) writes:
>
> >In article <1993Sep14.1...@oracle.us.oracle.com>, mfri...@us.oracle.com (Michael Friedman) writes...
> >>In article <CDC5u...@blaze.cs.jhu.edu> sti...@rhombus.cs.jhu.edu (Lewis Stiller) writes:
>
> >>>Hi, I have a question about The Billiard Ball. Given the premise that
> >>>objects in a zero-gravity field move at velocity c relative to the
> >>>spectators, I don't understand how the ball itself was accelerated to
> >>>this speed.
>
> >>Since I didn't read the story, I can't comment. The idea seems rather
> >>bizarre, however. We all know that a ball in 0 g just floats there.
>
> >Read the story. This is just the common misconception about 0g. Space is not
> >zero gravity. Objects still have mass in orbit, and are affected by the pull
> >of gravity. However, they are in constant freefall
>
> David, I suggest that you stop getting your physics from science
> fiction. Xg is convenient shorthand for the ratio between the weight
> of a point object in the circumstances being described and its weight
> at rest on Earth at sea level. (And please don't play games with the
> meaning of "at rest".) When we say someone (or something) is at 0g we
> mean that it undergoes no gravitational acceleration relative to the
> reference frame we are using. It has nothing to do with whether the
> object has mass or if they are affected by the pull of gravity.
> Moreover, your patronizing attitude is extremely irritating,
> expecially given your own apparent ignorance.
Michael, your criticism is absolutely uncalled for. Everything David said
is correct, and your elaboration is essentially a confirmation. David
correctly pointed out that many people have the false notion that objects
in orbit (at 0g) are not subject to the force of gravity, when of course it
is the force of gravity that keeps it in orbit in the first place.
Furthermore David's indignation was justified, since Lewis Stiller chose to
comment on a story he did not read, where the central premise of the story
is that a gravity-free region of space is created. Furthermore if you mean
to imply that the science in science fiction can never be trusted, you are
doing a disservice to science fiction writers who are also scientists (such
as Asimov was) who try to keep the science in their stories accurate
(although they sometimes take liberties, with the story in question being a
good example).
> >Something with zero mass, according to some equation
> >you can read about in _Asimov On Science: A 30 Year Retrospective_ in the
> >article "The Luxon Wall", must go at the speed of light or violate the laws of
> >physics. So the ball exits at the speed of light (after that come
> >the holes in the story, such as the particles would go in all
> >direction because of uncertainty, and the shock wave of it hitting
> >the wall would obliterate the whole city, but it still would go out at c.)
>
> Well, first off, the original question was about a 0g field, not a 0
> mass field. Secondly, I think that your ignorance is showing again.
Again uncalled for. Your definition of 0g does not match the situation
described in the story. If you read the story you should have realized
that, regardless of the wording of the original question.
> If entering the massless field instantaneously accelerates the ball to
> light speed shouldn't exiting instantaneously slow it back down?
> Moreover, unless out 0 mass field pumps and incredible amount of
> energy into the ball, the atoms in the ball will not have the energy
> to break their bonds. In fact, that makes sense. As the particles in
> the ball become massless the acceleration exerted by the
> electromagnetic fields in the ball should approach infinity. (F = ma.
> F stays constant, m-> 0, therefore, a -> oo). In short, we should
> expect the ball to stay together. It should travel to the edge of the
> field, accelerate to light speed as it traverses the edge, and then
> decelerate as it hits the other edge. No radiation, no sonic boom, no
> danger.
Here is where you science comes into question. Instantaneous
acceleration/deceleration? No change in energy? F=ma? I guess you are the
expert physicist here -- NOT! I won't go as far as to say you are ignorant,
since that crime of name-calling is what I believe you are guilty of, and I
would ask you to keep things a bit more civilized (and fun, if possible) if
you please. Thanks.
--
Ed Seiler
sei...@nibbles.gsfc.nasa.gov
"If puns are outlawed, only outlaws will have puns."
Jonathan DeMarrais
>
>
>Asimov knew perfectly well that the premise was scientifically wrong.
>It's Science Fiction, and for better or worse, in the genre we accept a
>certain amount of fast-and-loose handling of the science involved.
A thought just occurred to me on this thread. You make the object 0 mass
and it starts traveling at the speed of light. However, now it will
have mass again (massless particles moving at the speed of light
do have a mass). So what happens next?
--
--- Jay j...@pollux.usc.edu (University of Southern California)
What a depressingly stupid machine.
Marvin
Lewis Stiller
Ed Seiler <sei...@nibbles.gsfc.nasa.gov> wrote:
(long list of quotations deleted)
>Furthermore David's indignation was justified, since Lewis Stiller chose to
>comment on a story he did not read, where the central premise of the story
>is that a gravity-free region of space is created.
I normally make it a firm policy never to reply to ad hominem attacks,
but this comment...and coming from nasa.gov it's somehow more annoying
than the usual portal and neophytye flames to which most Usenet users
are inured.
I was the one who started this Billiard Ball thread. Thus I read the
story. I own and have read nearly all Asimov's science fiction corpus,
and have posted commentary on Asimov before. The person who said that
he didn't read the story but was commenting nonetheless was not I, as
you can verify by reading the original articles.
It's a good rule to double check attributions, especially in long
threads.
Rick Goyette
DeMarrais) wrote:
>
> A thought just occurred to me on this thread. You make the object 0 mass
> and it starts traveling at the speed of light. However, now it will
> have mass again (massless particles moving at the speed of light
> do have a mass). So what happens next?
I do not believe this is correct. A photon has no rest mass and travels at
the speed of light. It does, however act as if it had an inertial mass
which can be defined:
m = p/v = hn/c**2
where m is the mass of the photon, p is the momentum, v is the velocity, c
is the speed of light, n is the frequency and h is Planck's Constent.
We must here distinguish between the GRAVITATIONAL MASS of an object and
the INERTIAL MASS of an object. The gravitational mass of an object
determines the force it experiences due to the gravitational attraction of
another object. The inertial mass of an object determines it response to
an applied force. This leads to the conclusion that light should be
affected by gravity (which it is).
But any object that starts off with zero gravitational (rest) mass will
always have zero rest mass.
R. J. Goyette
RJGo...@anl.gov
Argonne National Laboratory
Chicago, Illinois
Ed Seiler
(Lewis Stiller) wrote:
> In article <seiler-21...@eseiler.stx.com>,
> Ed Seiler <sei...@nibbles.gsfc.nasa.gov> wrote:
>
> (long list of quotations deleted)
>
> >Furthermore David's indignation was justified, since Lewis Stiller chose to
> >comment on a story he did not read, where the central premise of the story
> >is that a gravity-free region of space is created.
>
> I normally make it a firm policy never to reply to ad hominem attacks,
> but this comment...and coming from nasa.gov it's somehow more annoying
> than the usual portal and neophytye flames to which most Usenet users
> are inured.
>
> I was the one who started this Billiard Ball thread. Thus I read the
> story. I own and have read nearly all Asimov's science fiction corpus,
> and have posted commentary on Asimov before. The person who said that
> he didn't read the story but was commenting nonetheless was not I, as
> you can verify by reading the original articles.
>
> It's a good rule to double check attributions, especially in long
> threads.
Sorry, I made a big mistake there. You are absolutely right, I should have
double-checked. The person who did not read the story was Michael Friedman,
not Lewis Stiller. I will be more careful in the future.
Tom O Breton
> You make the object 0 mass and it starts traveling at the speed of
> light. However, now it will have mass again (massless particles moving
> at the speed of light do have a mass).
You have to distinguish between rest mass (which your first case is) and
total energy (which your second case is)